Industrial nitrogen fixation was at the beginning of the 20th century, described as six different technology principles by J. W. Mellor, Inorganic and theoretical chemistry, “The fixation of atmospheric nitrogen” p. 366: (1) Fixation of nitrogen with oxygen in an electric arc plasma reactor. Birkeland-Eyde (B-E) and Schönherr; (2) The Calcium Cyanamid process. Reaction via calcium carbide. Frank-Caro; (3) The Barium Cyanide process. One step reaction with carbon and nitrogen; (4) Fixation of nitrogen with hydrogen on an iron catalyst. Haber-Bosch; (5) Absorption of nitrogen in metal with a reaction to ammonia when exposed to water; and (6) Nitrogen fixation in general combustion processes.
In the industrial development, the four first processes were dominating, and for a period they were competing. In the first process, the electric arc process reacted nitrogen with oxygen according to the reaction:N2+O2=2NO ΔHf=6.4 GJ/tN  I
The development of the ammonia process involved reacting nitrogen with hydrogen from water and air:3H2O(l)=3H2(g)+1.5O2(g) ΔHf=30.61 GJ/tN  II+N2(g)+3H2(g)=2NH3(l) ΔHf=−5.77 GJ/tN  III=3H2O(l)+N2(g)=1.502(g)+2NH3(l) ΔHf=24.84 GJ/tN  IV
The most competitive way to produce ammonia today is through steam reforming of methane, where the stoechiometric minimum is 18 GJ/tNH3 and best industry practice is 27-30 GJ/tNH3 corresponding to 33-35 GJ/tN. In this process the advantage is that the Hydrogen also comes from the energy source.
The first large scale production initiative applying electric arcs was carried out by “Atmospheric Air Products Company” in Niagara Falls. The process failed due to lower than expected yield and high power costs, and was closed after a short trial period.
The first direct nitrogen fixation that was able to deliver a potent contribution to the global fertilizer market was the Birkeland-Eyde process. “Norsk Hydroelektrisk Kvelstoff Aksjeselskap” was established in order to industrialize this process.
The B-E process was completely different from the other processes by the way it controlled the intensity of the electric arc by means of a magnetic field. The electric arc was shaped into a two dimensional disk. The air was fed into the plasma disk perpendicular through ceramic perforated plates on both sides of the disk. The air was leaving radially into the outer circular collection tube. The B-E process was easier to scale up, start up, operate and control compared to other processes.
The Schönherr process developed by BASF, was an electric arc in a tube reactor with heat recovery from a counter current heat exchange between feed and product gases. The tube reactor gave a better potential for operating under higher pressure. The Schönherr reactors were also installed at Notodden.
In the electric arc processes, the temperature in the arc was calculated to be in the range between 3000 and 4000 K. The yield was normally described by the percentage of NO achieved in the air outlet, and was from 1% to 2%.
The global research with several types of small-scale reactors had given higher yields, but most attempts to increase scale and capacity failed to meet the expectations.
The energy consumption for the B-E process was described as kgHNO3/kilowatt year. The energy consumption at 3200 K was 285 kgHNO3/kilowatt year, and this corresponds to 474 GJ/tN. This includes all industrial losses. The reactors were performing much better over short periods with close follow-up. The load per reactor also had a significant effect on the energy consumption. The high energy consumption was explained by the frames given for the reaction:                The high reaction temperature, 3000-4000 K was required for the dissociation of nitrogen.        The maximum yield was 2% NO in the air, which meant most of the energy was used for heating the air.        Heat recovery was not applied because of the extreme temperatures and the low value of the waste energy.        
The improvement potential was substantial and documented in the scientific environment. The consensus for how to significantly improve the process was:                Operating the process at higher pressure was known to give a higher yield of NO. The challenge was however to find the materials able to withstand the pressure and temperature.        Applying a catalyst for lowering the required temperature for cracking the N2 molecule.        
The following three Norwegian patents are supporting the initial industrial realization and development and are defining the basic features of the electric arc process.
Norwegian Patent 12961 of Feb. 20, 1903 is the original Birkeland method where the electric arc is shaped as a disc by the means of using a magnetic field and alternating the current. No performance data is given in the patent, but the industrial process gave 1-2% NO with a gross energy consumption of 300-500 GJ/tN.
Norwegian Patent 20487 of Jul. 22, 1908 by BASF, is describing that by direct contact cooling of the plasma, a yield of 9.5% to 14% is achievable. The contact cooling was achieved by lowering the pressure to expand the volume and external surface of the plasma. Energy consumption reported was 90 gHNO3/kWh=8.8 GJ/tN. The patent is referring to Journal of chemical Soc. 1897, vol 71, page 181 and is stating that the lowering of the pressure alone has no independent effect on the yield. The patent further claims that higher pressure is better for the conversion to NO, but the low pressure is required for the direct contact cooling, and to reduce the decomposition of NO.
Norwegian Patent 19862 of Jul. 9, 1909, by BASF, claims that by using an air cooled tube-shaped anode, it is possible to produce cold plasma. The patent claims that normal to slightly lower pressure is required to lower the temperature of the anode and produced plasma.
The next generation of patents is focusing on improving the individual and initial features with a variety of practical solutions.
Swiss Patent 105135 of Apr. 5, 1917 describes the use of several arcs arranged to give a continuous plasma arc which is further chilled by external gases alone or with gas containing solids. No performance data given.
British Patent 159709 of Mar. 10, 1921 describes a method of using magnetic fields to shape a nozzle-like electric arc. No performance data given.
U.S. Pat. No. 1,902,384 of Mar. 21, 1933 describes a method for shaping the plasma arc by means of a magnetic field without alternating the current. No performance data given.
U.S. Pat. No. 2,485,476 of October 1949 describes a method of combining high potential and low potential electrodes operating cyclically. The claimed effect being that through wavelength adjustment the yield can be optimized. One claim is also covering operation at a half atmosphere. Reported results range from 30 to 120 gHNO3, which corresponds to 135 to 540 GJ/tN.
British Patent 700,801 of Dec. 9, 1953 describes a method for achieving two plasma phases, one producing negative ions and the other producing positive ions, by high frequency alternation of the electric field. Mixing and extracting the mix from the plasma zone is further reducing the decomposition of the formed oxides. The performance data, gross outcome 14.5-115 gHNO3/kwh and net outcome 100-300 gHNO3/kwh.
British Patent 915,771 of Jan. 16, 1963 describes a method operating at excess of 400 mmHg, applying an alternating electric field of radio frequency, producing cold plasma. The process is applied for different processes. No results from the 400 mmHg operation for NO. From operating at 1 atm, 0.3% to 5% NO is reported with an energy consumption of 16-68 gHNO3/kwh.
U.S. Pat. No. 3,439,196 of Apr. 15, 1969 and U.S. Pat. No. 3,471,723 of Oct. 7, 1969 describe a conceptual full industrial process for producing nitric acid based on an improved process for supplying energy and recovering this in a magnetohydrodynamic generator. The process is operating at above atmospheric pressure. There are no documented results in the patents.
U.S. Pat. No. 3,666,408 of May 30, 1972 describes a process where the oxygen and nitrogen plasma is made and expanded into a mixing zone. The patent is superseding U.S. Pat. No. 805,069 of Dec. 27, 1968 and U.S. Pat. No. 639,880 of May 19, 1967. The applied expansion ratio ranges from 30:1 to 200:1. The lowest energy consumption reported for this process is 2000-3000 BTU/lb of gas treated, which corresponds to from 86 to 130 GJ/tN. The additional energy consumption for air separation and compression seems to give this process unacceptable and unavoidable energy consumption.
U.S. Pat. No. 4,267,027 of May 12, 1981 describes a process for preparation of nitrogen oxides by quenching plasma formed in an unspecified plasma torch. The quench is consisting of catalyst surface cooled by external coils. There are no documented results in the patent.
U.S. Pat. No. 4,705,670 of Dec. 10, 1987 describes a principle for distributing micro-discharges over an electrically conductive liquid, where the formed NO shall be absorbed in the liquid. There are no documented results in the patent.
U.S. Pat. No. 4,877,589 of Oct. 31, 1989 describes a process with an electric arc operating inside a bed of catalyst, the catalyst being various kinds of high temperature resistant materials. The claimed effects are shielding of the ultraviolet light, the creation of turbulence and the distribution of heat. There are no documented results in the patent.
U.S. Pat. No. 4,833,293 of May 23, 1989 describes an electric plasma nitrogen reactor with a sort of path heat transfer principle. The principle consists of a heat capacity pebble principle combined with a pulsating reverse flow principle. There are no documented results in the patent.
The three oldest conceptual patents are the Norwegian patents 12961, 20487 and 19862 from the period of 1903-1909. These patents are from the two companies who contributed to the industrial realization of the electric arc technology. These three patents describe with limited details two independent effects.
NO12961 describes the use of a magnetic field to expand the surface and contact phase between the arc and air and in that way release high amounts of energy into a large volume of air.
NO20487 applies lower pressure to reduce the energy intensity and temperature of the plasma to facilitate contact cooling of the arc itself. The patent is referring to Journal of chemical Soc. 1897, vol 71, page 181 and is stating that the lowering of the pressure alone has no independent effect on the yield.
NO 19862 describes applying lower pressure to reduce the energy intensity and temperature. The yield is described to be higher with higher pressure. The only claim is cooling of the arc and electrode by sending air through the hollow electrodes.
Prior art has further focused on solving the material and temperature challenges, and can be grouped in:                Applying a magnetic field to move the arc through the air to give large plasma volume with a lower temperature.        Increasing the pressure to obtain a higher NO yield.        Lowering the pressure to expand the arc and plasma volume to achieve a lower temperature.        Quenching with air mixing, water spray or with a gas with solids to create colder plasma.        Cooling with direct contact in a cooler.        
Prior art has not been able to improve the yield and energy efficiency significantly from the first proven technology from 1900-1910. The splitting of the Nitrogen molecule requires high temperature and high energy intensity. The high temperature is a challenge for the materials containing and cooling the arc and plasma.
The challenge has been to design a process where the high temperature arc can split a high fraction of the Nitrogen molecules and where the created plasma can be stabilized and cooled without damaging the containment materials.
The thermodynamic properties of the reactants and reaction products have apparently also been an obstacle for developing the process further.
Applying Gibbs free energy and Arrhenius to find the equilibrium for the reaction I,N2+O2=2NO, ΔGf for NO=86.55 kJ/mole  Ishows that at 3500K the equilibrium NO concentration is only 2.0%. The temperature has to be raised to 9000K before the NO concentration will reach 10%. Heating the air to from 2000 to 3000K corresponds to presented energy consumption of 200-360 GJ/tN. This is enough to discourage most chemists from believing that this process can be feasible. This is also why several patents and concepts have been abandoned.